Biology 11
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Transcript of Biology 11
Biology 11
Kingdom PlantaeThe Gymnosperms
By the end of the lesson you should be able to: Compare and contrast bryophytes,
pteridophytes and gymnosperms Describe the lifecycle of a gymnosperm Give examples of gymnosperms
Objectives
Evolution of Seeded Vascular Plants
When the Mesozoic era got under way, it ushered in a time of geological and climatic instability
Continental drift formed the “super continent” called Pangea
Cooler and dryer conditions put survival pressure on the water dependent non seeded vascular plants
The key to survival was surviving without water
Evolution of Seeded
Vascular PlantsIn plants, this resulted in three significant advances:1. Gametophyte reduced even more and becomes protected and completely dependent upon sporophyte 2. Asexual spores evolved into sexual pollen for air distribution of the gametes3. Development of an embryo protecting
mechanism (seeds) that also could more effectively distribute their species
Gymnosperms: seeded vascular
plants First evolved in Paleozoic Changes in the Mesozoic
made this their era Dominant during this time
were the ginko and cycads
A cycad
Early Gymnosperm:
Ginkgo
Early Gymnosperm:
cycads
Gymnosperms
The Conifers These are our familiar evergreen trees and
shrubs They lived in the dry continental interiors When the climate changed at the end of the
Mesozoic, the conifers were pre-adapted and flourished
Common Gymnosperm: Conifers
Gymnosperms They are still the dominant plant in the
north temperate zones They are the dominant biome in Canada
called Boreal or Taiga coniferous forests
Gymnosperms
The sporophyte has become very dominant It is utilizing all of the advantages so far
evolved
Seeded Vascular Plants Gymnosperm: conifers
vascular heterospory
male vs. female gametophytes seeds
naked seeds (no fruit) pollen
contain male gametophyte life cycle dominated by sporophyte stage
coniferous trees you are familiar with are diploid reduced (microscopic) gametophyte reduction of gametophyte protects delicate egg &
embryo in protective sporophyte protected from drought & UV radiation
Gymnosperms
Advances: True roots are seen for the first time which
allows the gymnosperms to live in dryer conditions
They no longer need water for reproduction Leaves are modified into needles The resins inside the needles act as a natural
antifreeze As a result, they became (and are) the
dominant tree of the north temperate zones
Male Cones
The male gametophyte is the pollen grain formed by meiosis inside the male cone
The male cone is small and short lived, dropping off the tree after a few weeks
The female gametophyte
is the egg formed by meiosis inside the female cone
After fertilization the female cone houses the seeds until next spring
The female cone is large and long lived, dropping off the tree after 2 years!
Female Cones
Cones & naked seeds
male
female
male (pollen) cones
female cones
sporangium & pollen
pine embryo
Pollen
Pollen eliminated the requirement for water for fertilization spread through wind
& animal
Where canconifers live?